Hepatocellular carcinoma (HCC) is one of the most common human malignancies and the third cause of death from cancer worldwide. Exposure to different hepatotoxins causing liver injury and DNA damage is the major risk factor of HCC. This proposal is focused on the role of p53 and p53-inducible Sestrin1 (Sesn1) and Sestrin2 (Sesn2) genes in protection against hepatotoxin-induced liver injury and hepatocarcinogenesis. During the last, 8 years I identified and characterized a novel Sestrin gene family, where Sesn1/2 genes are p53-dependent stress responsive genes involved in regulation of reactive oxygen species, the protection against oxidative stress, and the suppression of mTOR signaling. The activation of Sesn1/2 genes can inhibit cell growth and induce autophagy. For a long time our lab has used a model of diethylnitrosamine (DEN)-induced hepatocarcinogenesis. DEN-treatment induces liver injury, oxidative stress, inflammation and DNA damage, which contributes [sic] to HCC formation in mice. Our lab has shown that the factors mitigating liver damage inhibit HCC development. DEN-exposure activates p53 and induces Sesn1/2 genes in liver. Surprisingly, p53-deficiency augments liver injury. Furthermore, DEN-treatment inhibits mTOR signaling, an important regulator of autophagy, in Sesn2-dependent manner. I hypothesize that p53 and Sesn1/2 genes can suppress HCC formation through activation of autophagy, mitigation of liver injury, and inhibition of oxidative stress. Additionally they can suppress HCC progression by inhibiting angiogenesis and metabolic switch toward glycolisis [sic]. To study the role of p53 and Sesn1/2 genes in DEN-induced stress response and hepatocarcinogenesis I will: 1) Evaluate the role of p53 and Sesn1 12 genes in DEN-induced stress response and HCC formation. Using mouse strains with deficiency p53 and Sesn1/2 in liver, I will characterize the role of these genes in DEN-induced autophagy, cell death, and compensatory proliferation as well as the signaling pathways involved in regulation of these processes. 2) Determine whether autophagy protects against liver damage and HCC formation. To adress [sic] this aim I will examine the autophagy-impared [sic] Beclin1 mice. 3) Examine the role of p53 and Sesn1/2 genes in suppression of different stages of HCC development, will use mice with tamoxifen-regulated expression of Cre-recombinase to delete p53 and Sesn1 genes in time-controlled manner. 4) Define if antioxidants and mTOR inhibitor can reverse the effect of p53 and Sesn1/2 deficiency on stress response and hepatocarcinogenesis. These finding regarding potential involvement [sic] of p53 and Sestrins in liver carcinogenesis can be used for diagnosis of human HCC. Also these results will provide the potential value of p53 and Sestrins as targets for therapeutic interventions.